The present invention relates to a device intended to allow applying a measurable pressure, pre-established within strict tolerances, onto an operating roller. This device can find particular, but not exclusive, application in exerting an operating pressure onto the counterroller or pressure roller of a spreading unit.
The thickness of the material layer spread onto a strip by means of a spreading unit depends mainly on the distance between the facing cyclindrical surfaces of the spreading roller and the counterroller or pressure roller of the spreading unit and hence, the other conditions being equal, on the pressure with which the counterroller is pushed towards the spreading roller. To control and to determine in advance the thickness of the material to be spread, it is a common practice to use mechanical stops intended to pre-establish the position of the counterroller, or manometers which measure the feeding pressure of air cylinders by means of which the counterroller is pushed towards the spreading roller. However, these devices allow measuring, and hence pre-establishing, the working conditions only in an approximate manner, both because of the large inertial masses involved and the presence of variable clearances and frictions.
The insufficiency of the known devices appears especially in spreading very thin layers, as for example in spreading silicones without solvents, where the application of a layer from 0.5 to 1.5 grammes per square meter, corresponding to a thickness from 0.5 to 1.5 micrometers, is required. Since it is not practically possible to directly measure either the mass or the thickness of the material applied in such a thin layer onto the strip which is being produced, these values can be determined only after application, by calculating them on the basis of the knowledge of the strip surface on which the material has been spread and the mass of material consumed in the course of the operation. Therefore, it becomes very important, to the effects of repeatability of the working conditions, to know and predetermine with considerable precision the pressure exerted onto the pressure roller of the spreading unit.